1. Field of the Invention
The present invention relates to a mobile station (apparatus) for communication with a satellite.
2. Description of the Related Art
Generally, in a cellular mobile communication system, a service area is divided into a plurality of coverage areas defined by a plurality of base stations. Therefore, when a mobile station moves from one coverage area to another coverage area, a complex call connection control is required. In addition, large blind areas due to the locations of the base stations may be generated, so that a service interruption is created for the mobile stations. In order to dissolve such problems, a mobile satellite communication system where mobile stations can communicate with each other via one or more satellites has been developed.
In a mobile satellite communication system using a plurality of satellites, one satellite may have a relatively large elevation angle with respect to a mobile station, while another satellite may have a relatively small elevation angle with respect to that mobile station. In addition, the mobile station may be located in a blind area of some of the satellites due to buildings or the like. Therefore, a prior art mobile station (apparatus) adopts a single omnidirectional antenna.
In the above-mentioned prior art mobile apparatus, however, it is impossible that the single omnidirectional antenna can have a uniform directivity over an elevation angle of from 0.degree. to 90.degree.. Even if the single omnidirectional antenna establishes a broad directivity, the antenna gain is 0 dBi at most. Therefore, if the antenna gain is forced to be increased, a transmitter circuit (power amplifier) has to be increased in size, thus increasing the manufacturing cost as well as the power dissipation. If the power dissipation is significantly increses, the continuous operation time period of the mobile apparatus is remarkably reduced.
In a system other than in a mobile satellite communication system, note that antenna diversity technology using a plurality of antennas in a receiver side has been used. However, even if antenna diversity technology is applied to a transmitter side, since the frequency of the transmitter side is different from that of the receiver side and the characteristics of the transmitting and receiving antennas are different from each other, this antenna diversity technology is not suitable in the transmitting side.